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Studies on the Topography of Biomembranes: Regioselective Photolabelling in Vesicles with the Tandem Use of Cholesterol and a Photoactivable Transmembrane Phospholipidic Probe

1996; Wiley; Volume: 2; Issue: 2 Linguagem: Inglês

10.1002/chem.19960020204

1521-3765

Yôichi Nakatani, Masakuni Yamamoto, Yvonne Diyizou, William Warnock, Valérie Dollé, Wolfgang Hahn, Alain Milon, Guy Ourisson,

Porphyrin and Phthalocyanine Chemistry

Abstract 2 H NMR, DSC and UV studies of DMPC (1,2‐dimyristoyl‐ sn ‐glycero‐3‐phosphocholine) vesicles have demonstrated the favourable physicochemical properties of the transmembrane phospholipid probes 1 a and 1 b for membrane topographical studies. In particular, in the presence of a physiological amount of cholesterol, only one transmembrane conformation is observed. The use of 1 a and cholesterol together for photolabelling experiments in DMPC vesicles led to a remarkable improvement in the regioselectivity of cross‐linking between 1 a and DMPC, and between 1 a and cholesterol: the myristoyl chains functionalized at C11, C12 and C13 made up 95% of the total photolabelled myristates, and cholesterol was principally functionalized at the C25 position on the side‐chain. This indicates the formation of a highly ordered bilayer structure and proves directly the orientation of cholesterol perpendicular to the membrane plane with its chain terminal buried in the middle of the bilayer.